VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.

  #1  
Old 11-30-2015, 10:33 PM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
 
Join Date: Jul 2009
Location: Mojave
Posts: 4,841
Default Experimenting With Ignition Timing

Much has been written on this forum concerning the pros and cons of electronic ignition and more specifically, the level of advanced timing they offer. Plenty of testimony that Lycomings "like" more timing than offered by the fixed magneto, and plenty of testimony that the factory knows best. There has also been dyno testing between the two, but the results have been less than convincing for either side. The current crop of electronic ignitions have fairly limited to zero adjustability and the curve seems somewhat mysterious. In my mind, what is needed is a completely adjustable ignition which you can tweak on the fly. Being able to set power, then move the timing around to see where the engine is happiest should put the issue to bed, shouldn't it?

Well, I have just installed an electronic ignition with that capability and I have done some preliminary testing. First off, the ignition is the new CPI product from Ross Farnham and it offers essentially an infinitely adjustable advance curve for RPM as well as a second curve based on MP. This system replaces one of the Slicks on my Rocket. On the first flight I set up a conservative advance essentially duplicating the 26 degree timing of the magneto and was able to replicate my typical cruise performance. Without touching anything but the ignition advance I was able to pick up a few knots of speed. The second flight was a data gathering flight to see if it was a fluke. The performance repeated.

Attached is a table transcribing the hand written notes from that flight. The method of testing was to get the airplane set up at cruise altitude, on autopilot and with a typical power setting (in this case, slightly LOP). I started at 26 degrees advance (duplicating the magneto timing) as my "baseline". Once stable, I would punch in some advance, let the ship stabilize, and then write down the results. Each change would stabilize in about 30 seconds, so I was able to cycle through the whole test in one 20 minute flight.

This is still very preliminary and some of the individual measurements dont track exactly as one would expect, but the overall trend is obvious. I thought it interesting enough to share. There will be much more testing shortly.

__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C

Last edited by Toobuilder : 11-30-2015 at 10:40 PM.
Reply With Quote
  #2  
Old 11-30-2015, 10:49 PM
F1Boss's Avatar
F1Boss F1Boss is offline
 
Join Date: Aug 2006
Location: Taylor Texas
Posts: 847
Default One change begets another!

Well, looks like your CHTs are kinda cold - now you will have to fab up some way to close off the outlet to bring 'em up in cruise, but keep 'em cool in climb. ARRGHH! ;-)

195KTAS on 11.5GPH is pretty good for that airframe. What is your compression?

I gotta hear more about this system - I expect good things from Ross. Good luck with the testing!

Carry on!
Mark
Reply With Quote
  #3  
Old 11-30-2015, 10:55 PM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
 
Join Date: Jul 2009
Location: Mojave
Posts: 4,841
Default

Yes, way too cold now. All that work to keep it alive in the desert summer heat is really hurting me now. It was 16 degrees F this morning on the way to work - two months ago it was 116. This airplane needs a cowl flap!

Engine is a factory stock -D4A5 (260 HP).
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
Reply With Quote
  #4  
Old 12-01-2015, 07:00 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,346
Default

Good stuff Mike.

May I suggest an experiment? Set up the same test as above (LOP cruise), run the four timing settings, then repeat them with the mixture richened to 100 ROP for the leanest cylinder.

If theory holds, the highest TAS will found with less advance...like 30~32 rather than 35.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #5  
Old 12-01-2015, 07:16 AM
drill_and_buck's Avatar
drill_and_buck drill_and_buck is offline
 
Join Date: Feb 2005
Location: Bridgewater, MA - KPYM
Posts: 479
Default How low should you go?

Like most of RVers I have been focused on managing the upper limits of CHTs. I have never given much thought to the lower end and was under the belief that 290 -310 were acceptable temperatures for cruise.

You now you have me thinking, "How low should you go?" I haven't been able to find any good data points on the implications of cruising with CHTs below 300 degrees.

What are the implications of cruising with low CHTs and how low should you go?

Data points, experience and opinions are appreciated.


Tks,
MD
__________________
Mike Draper
RV-8 N468RV
First Flight 11/13/2011
TMX0360, Dual Pmags, CS
Reply With Quote
  #6  
Old 12-01-2015, 07:24 AM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
 
Join Date: Jul 2009
Location: Mojave
Posts: 4,841
Default

Sure thing Dan, next time I fly. (Probably Friday)

Along those same lines (less advance needed with a rich mixture), I'm also going to deterrmine if the engine likes less than stock timing at TO power. That one is going to be tough though - flying along at 500 MSL at 99% power while messing with the ignition box is going to require some concentration. Probably best to head out to the coast... Dont need to tangle with power lines at 220 knots!
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
Reply With Quote
  #7  
Old 12-01-2015, 07:35 AM
Weasel's Avatar
Weasel Weasel is offline
 
Join Date: Dec 2012
Location: Brooksville, MS
Posts: 750
Default

Your results are very similar to mine.

I have a single Bendix Mag and a Lightspeed ignition.

The engine is a IO-540C4B5 (Identical to yours except mine is narrow deck) with ~9.2:1 CR.

I have the optional potentiometer connected to the Lightspeed and can adjust the timing in flight.

I have found it much the same. My baseline timing is a little lower due to higher compression. I start at about 23 deg at max power and advance to around 29 degrees at the same cruise conditions that you tested. Any more timing than that and it starts to drop speed but as long as I am running 100LL it will not detonate with a lot more timing.

During the summer months when summer mogas was available with a 9 PSI RVP I ran 93 octane non-ethanol but had to limit the advance to around 26 deg due to higher compression. Now that the Mogas here has switched to winter (13 PSI RVP) gas I am back on 100LL.
__________________
Weasel
RV-4 715hr Sold
RV-10 "School Bus" - +1700hr counting
RV-10 N7631T 820hr Sold
RV-8 700+hr
SERFI AWARDS

http://weaselrv10.blogspot.com/
Reply With Quote
  #8  
Old 12-01-2015, 07:39 AM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
 
Join Date: Jul 2009
Location: Mojave
Posts: 4,841
Default

Quote:
Originally Posted by drill_and_buck View Post

...What are the implications of cruising with low CHTs and how low should you go?

Data points, experience and opinions are appreciated...
My understanding is that IC engines are heat difference devices. The more heat that turns to power is more efficiency. Generally, the hotter the better - as long as you stay within the thermal limits of the materials the engine is made of. You may recall the interest in ceramic engines some years ago. That was an attempt to get an engine to survive at much higher temperatures than available today. Consider also the evolution of the gas turbine engine. The basic architecture of jet engines has not changed all that much, but yet we have seen radical gains in output/efficiency with every new generation. This is significantly attributable to increasing TIT (turbine inlet temperature), or more specifically, the ability to keep the hot section parts alive.

Just my opinion, but I would be very happy if I could maintain a CHT of 350-375 in all phases of flight, year round. I also think my engine would be happy as well.

All that said, my sub 300 CHT is not due to the change to this ignition - it was doing this last winter as well. LOP ops and sub freezing OAT will do that to you.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C

Last edited by Toobuilder : 12-01-2015 at 07:45 AM.
Reply With Quote
  #9  
Old 12-01-2015, 08:12 AM
Tom Martin Tom Martin is offline
 
Join Date: Jan 2005
Location: Ontario, Canada
Posts: 1,591
Default

I have one bendix and one light speed as well. I can not manually adjust my light speed, but I do have a readout, and at similar flight conditions my advance is 32 degrees. I believe this is the maximum allowed by the lightspeed?
The one difference is that I run at best power settings for 65% or less power settings. I have not found the difference between total gallons used on a trip between LOP and best power settings, at altitude, to be worth the extra time.
Dan has suggested a 100 ROP, why not include one at best power to see if there is any difference? At these power settings you should be within the reccomended Lycoming power range for best power.
__________________
Tom Martin RV1 pilot 4.6hours!
CPL & IFR rated
EVO F1 Rocket 1000 hours,
2010 SARL Rocket 100 race, average speed of 238.6 knots/274.6mph
RV4, RV7, RV10, two HRIIs and five F1 Rockets
RV14 Tail dragger

Fairlea Field
St.Thomas, Ontario Canada, CYQS
fairleafield@gmail.com
Reply With Quote
  #10  
Old 12-01-2015, 08:17 AM
David-aviator David-aviator is offline
 
Join Date: Feb 2005
Location: Chesterfield, Missouri
Posts: 4,514
Default

Intersting information Mike. Thanks.

The EFII system I installed is limited to 30? advance. I believe most EI systems will go to at least 35? which is probably more optimal LOP above 10,000. The CAFE testing years ago seemed to conclude up to 8000 mags were just about as efficient as EI, but up higher they fall off due to fixed timing. Your testing would indicate that may not be true.

There is a good reason timing is not adjustable in flight - it requires attention and if not done properly the consequences could be expensive. So one needs to be careful and know whats going on - like flying LOP.

I like advanced timing down low at low power. The Lycoming probably would be just fine at 37? - clean plugs, no unburnt fuel and LOP. I co not have that feature, 30? is max advance.
__________________
RV-12 Build Helper
RV-7A...Sold #70374
The RV-8...Sold #83261
I'm in, dues paid 2019 This place is worth it!
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 11:18 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.